Datasheet

596
32117D–AVR-01/12
AT32UC3C
25.6.7 Modem Mode
The USART features modem mode, which enables control of the signals: DTR (Data Terminal
Ready), DSR (Data Set Ready), RTS (Request to Send), CTS (Clear to Send), DCD (Data Car-
rier Detect) and RI (Ring Indicator). While operating in modem mode, the USART behaves as a
DTE (Data Terminal Equipment) as it drives DTR and RTS and can detect level change on DSR,
DCD, CTS and RI.
Setting the USART in modem mode is performed by writing the MODE field in the Mode Regis-
ter (MR) to the value 0x3. While operating in modem mode the USART behaves as though in
asynchronous mode and all the parameter configurations are available.
Table 25-12 gives the correspondence of the USART signals with modem connection standards.
The control of the DTR output pin is performed by writing the Control Register (CR) with the
DTRDIS and DTREN bits respectively at 1. The disable command forces the corresponding pin
to its inactive level, i.e. high. The enable command forces the corresponding pin to its active
level, i.e. low. RTS output pin is automatically controlled in this mode
The level changes are detected on the RI, DSR, DCD and CTS pins. If an input change is
detected, the RIIC, DSRIC, DCDIC and CTSIC bits in the Channel Status Register (CSR) are set
respectively and can trigger an interrupt. The status is automatically cleared when CSR is read.
Furthermore, the CTS automatically disables the transmitter when it is detected at its inactive
state. If a character is being transmitted when the CTS rises, the character transmission is com-
pleted before the transmitter is actually disabled.
Table 25-12. Circuit References
USART Pin V24 CCITT Direction
TXD 2 103 From terminal to modem
RTS 4 105 From terminal to modem
DTR 20 108.2 From terminal to modem
RXD 3 104 From modem to terminal
CTS 5 106 From terminal to modem
DSR 6 107 From terminal to modem
DCD 8 109 From terminal to modem
RI 22 125 From terminal to modem